Optimization Of Cementitious Conductive Electrode Loaded With Pt/Bi And Its Application In Wastewater Treatment

Electrochemical oxidation treatment could effectively remove the organic matter and ammonia nitrogen in the leachate and improve the biochemical property of the leachate?BOD₅/COD?.Electrode material is the most important factor that affects the efficiency of electrochemical oxidation,the search of a high catalytic performance and economic benefits electrode material becomes the focus of electrochemical oxidation method.Pt-Bi/CAG electrode,Pt-Bi/CFAG electrode and Pt-Bi/CFAG-rGO electrode were prepared by the optimization of electrode materials using response surface method and doped fly ash and graphene.The differents of electrode performances were compared,and the efficiencies of electrochemical oxidation of methyl orange?MO?,ammonia nitrogen simulation wastewater and landfill leachate were analyzed.The experimental results were as follows:?1?The optimal preparation mass ratio of Pt-Bi/CAG electrode was cement:activated carbon:graphite powder=5:4:1,and the material was loaded on the eight-hole square type perforated graphite paper.The electrode had the highest specific capacitance which was up to 29.56 F/cm².The Pt-Bi/CAG electrode was applied to 150 mL 20 mg/L MO for a period of 3 h electrochemical oxidation process.The optimal electrodeposition voltage was-0.8 V,the electrodeposition time was 240 s,the electrodeposition voltage was±1.5 V,the pulse time was 60s.In this case,the degradation rate was 84.6%and gradually stable at 60%in the second,third and fourth cycles of MO degradation.The amount of Pt-Bi particles on the electrode surface was decreased in the degradation process,and the electrode was seriously damaged.When[Cl^-]in MO solution reached 400 mg/L,Pt-Bi/CAG electrode could almost completely degrade MO in 3 h.?2?The optimal material ratio of Pt-Bi/CAG electrode?mass ratio?was cement:fly ash:activated carbon:graphite powder=45:30:15:10,the electrode ratio capacitance is the highest?34.86 F/cm²?and the firmness was also improved to 0.478 N.In the degradation process of 150 mL 20 mg/L MO,it was found that the optimal electrolytic condition was in the parameters of-0.8 V electrodeposition voltage,240 s electrodeposition time,1.5 V electrolytic voltage,and 60 s pulse time.At this time,the degradation rate of MO within 3 h was the highest which was 71.27%and maintained at about 45%in the further degradation process.The Pt-Bi particles on the electrode surface were gradually decreased with the electrolysis time.When the concentration of Cl^-in MO solution reached to 400 mg/L,MO is almost completely degraded within 3h.?3?When the doping amount of graphene was reached to 0.25%,the firmness of Pt-Bi/CFAG-rGO electrode was improved to the maximum,which was 0.998 N.At the same time,the electrode specific capacitance was also the largest,which was 39.14 F/cm².The best degradation parameters of 150 mL 20mg/L MO were 240 s electrodeposition time,-1.0 V electrodeposition voltage,3.0 V electrolytic voltage,and 60 s voltage pulse time,the degradation efficiency of MO was the best,reaching 91.16%within 3h,and was stable at 53%in the consecutive forth cycles of MO degradation.After four cycles,there was no obvious crack on the electrode surface,and the electrode remained firm.When the concentration of Cl^-in MO solution reached to 400 mg/L,it was almost completely degraded within 3 hours,and the higher the concentration of Cl^-,the larger the pore size of the electrode surface and the higher the electrode erosion degree.?4?Pt-Bi/CFAG electrode and Pt-Bi/CFAG-rGO electrode were used for electrolysis of ammonia nitrogen water with the initial ammonia nitrogen concentration and pH was 42 mg/L and 7.2,respectively.Ammonia nitrogen degradation rate was almost 0 without adding Cl^-and adjusting pH.For Pt-Bi/CFAG electrode,and ammonia nitrogen was almost completely degraded in the Cl^-concentration of 600 mg/L.For Pt-Bi/CFAG-rGO electrode,when the concentration of Cl^-was added to 500 mg/L,ammonia nitrogen was almost completely degraded.pH also has an effect on the degradation of ammonia nitrogen.The best ammonia nitrogen degrading efficiency was obtained at the pH of 11 which was 41.89%and 44.02%by Pt-Bi/CFAG electrode and Pt-Bi/CFAG-rGO electrode.?5?Landfill leachate was degraded by Pt-Bi/CFAG electrode and Pt-Bi/CFAG-rGO electrode,respectively.The optimal electrolytic parameters of Pt-Bi/CFAG electrode were electrodeposition time of 240 s,electrodeposition voltage of-0.8 V,square wave voltage of±2.5 V and 60 s pulse time,and the COD removal rate reached 52.58%within 3 h.The optimal electrolytic conditions of Pt-Bi/CFAG-rGO electrode were 240s electrodeposition time,-0.8V electrodeposition voltage,±2.0 V square wave voltage,and 60 s pulse time,in which the COD removal rate reached 50.08%within 3 h.Adding 15 mg/L of PFS to the landfill leachate for coagulation pretreatment,followed by four cycles of electrolysis,the results showed that the removal rate of COD in the leachate with Pt-Bi/CAFG electrode was 88.7%,meeting the second grade emission standard.However,with Pt-Bi/CFAG-rGO electrode,the COD removal rate was reached to 92.2%,and closer to the first emission standards.Moreover,Pt-Bi/CFAG-rGO electrode had significant economic benefit compared with other common electrodes applying in landfill leachate.